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Clinical manifestations and diagnosis of avian influenza

Iain Stephenson, MD, FRCP
Section Editor
Martin S Hirsch, MD
Deputy Editor
Anna R Thorner, MD


There have been five influenza pandemics during the past 100 years, and each has been caused by the emergence of a novel virus. In the 1957 and 1968 pandemics, the new viruses contained components of previous human as well as avian influenza viruses. The origin of the influenza virus responsible for the 1918 pandemic, which killed more people in a single year than the bubonic plague, remains uncertain, but it appears to have been an adapted avian influenza strain. The emergence of a novel H1N1 human-swine-avian reassortant virus in 2009 in North America started a new pandemic. (See "Epidemiology of pandemic H1N1 influenza ('swine influenza')".)

Sporadic transmission of avian influenza H5N1 to more than 850 humans since 2003 has prompted concerns that conditions are suitable for emergence of a pandemic strain [1]. Two features of avian influenza H5N1 outbreaks are striking: the predominance of children and young adults; and the high mortality rate [2,3]. However, seroprevalence studies have found that some exposed individuals may have had a subclinical or mild infection, suggesting that the reported case-fatality rate may be an overestimate.

The clinical manifestations and diagnosis of avian influenza will be reviewed here. The epidemiology, transmission, pathogenesis, treatment, and prevention of avian influenza are discussed separately. (See "Epidemiology, transmission, and pathogenesis of avian influenza" and "Treatment and prevention of avian influenza" and "Avian influenza vaccines" and "Avian influenza A H7N9: Epidemiology, clinical manifestations, and diagnosis".)


The clinical manifestations of avian influenza are variable, being determined in part by the virus clade.

Avian influenza H5N1 — More than 850 human cases of H5N1 influenza have been reported to the World Health Organization, with a case-fatality rate of approximately 53 percent [1]. Most patients with H5N1 infection give a history of recent exposure to dead or ill poultry. H5N1 infection can result in mildly symptomatic illness to life-threatening disease. The clinical presentation may depend on the duration of exposure and the clade of the virus [4-8].

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Literature review current through: Nov 2017. | This topic last updated: Nov 02, 2017.
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